The U.S. Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the U.S. Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory.
The invention described herein relates generally to microwave detectors, and more particularly to detectors for measuring high-frequency component microwave pulses.
There exist many detectors and detector systems for measuring the frequency and power of most ordinary microwave signals. These known detectors and systems are described in many textbooks, one of which is "Handbook of Microwave Measurements, Third Edition (1963)" by M. Sucher and J. Fox, published by the Polytechnic Press of the Polytechnic Institute of Brooklyn, which is hereby incorporated by reference herein.
Some microwave devices contain ferrites. Ferrites are magnetic materials that are described in many textbooks, one of which is "Principles of Microwave Ferrite Engineering (1969)" by J. Helszajn, published by Wiley-Interscience, which is hereby incorporated by reference herein.
A ferrite microwave detector is described by Jaffe et al in Proceedings of the IRE, vol. 46, pages 594 to 601, 1958. In this mechanical-type detector, the demodulated envelope of an amplitude-modulated microwave signal is used to magnetostrict a long thin ferrite rod. The mechanical vibration of the ferrite rod is observed by means of a ferroelectric transducer bonded to the end of the ferrite rod or by a coil wound around the ferrite rod.
A very well known and much used microwave detector is the B-dot sensor. In essence, this detector simply comprises a conducting metal loop disposed within the microwave signal environment so that the integrated magnetic field passing through the loop changes with time and induces an electrical signal which is recorded by means usually involving a cable system coupled to both the conducting loop and an oscilloscope. A balanced output may be achieved by adding a second B-dot sensor in the opposite orientation from the first, and by using a balun circuit for the difference signal to eliminate common spurious signals in the usual way. Thus the word dot in the name of this detector refers to the time derivative of the magnetic field B. The B-dot detector is ineffective at microwave frequencies above about 3 GHz, because the cable response characteristics of the recording system preclude the transmission of such high frequency signals, which average to zero over time, to the recording oscilloscope. If the B-dot detector is used in attempting to measure a microwave pulse comprised of such high frequency microwave oscillations, the recording oscilloscope will not display any measured trace. In this situation it would be very beneficial to be able to measure the shape of the pulse envelope of the high-frequency oscillations actually comprising the pulse.
Semiconductor type microwave detectors do exist which can record very high frequency microwave oscillations. However, these detectors are extremely sensitive and delicate, and they often require a primary signal attenuation of many orders of magnitude which makes their calibration very difficult. These semiconductor type detectors, furthermore, can burn out when subjected to merely a few watts of extraneous electromagnetic-pulse power. Another disadvantage of these semiconductor type microwave detectors is that they produce very small output voltages and thus often require amplifiers. These amplifiers, also, are very sensitive to small extraneous pulses of electromagnetic power and can easily burn out.